Data storage devices of the type known as "Winchester" or "hard" disc drives are typically provided with a plurality of rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. A controllably positionable actuator is disposed adjacent the discs, the actuator including a plurality of heads which are used during write and read operations to store and retrieve user data from tracks defined on the disc surfaces.
A closed loop servo system is used to control the position of the heads with respect to the tracks on the disc. More particularly, the actuator typically includes a coil of a voice coil motor (VCM) so that currents applied to the coil by the servo system cause the heads to move relative to the tracks in a controlled manner. A read/write channel, responsive to the heads, controls the transfer of user data between the discs and a host computer in which the disc drive is mounted.
As will be recognized, advances in the disc drive industry have led to continual increases in disc drive storage capacities and data transfer rates, necessitating ever increasing complexity in the control systems used to maintain proper operation of the drives. Accordingly, compensation routines for various disc drive systems have been developed so that disc drives can achieve optimum performance in light of changes in operational and environmental conditions. Typical compensation routines are disclosed by, for example U.S. Pat. No. 5,566,095 entitled FAST CALIBRATION USING MICROSTEPS, issued Oct. 15, 1996 to Cameron et al. (servo gain calibration); U.S. Pat. No. 5,585,976entitled DIGITAL SECTOR SERVO INCORPORATING REPEATABLE RUN OUT TRACKING, issued Dec. 17, 1996 to Pham (compensation for repeated run out components in servo position error signals); U.S. Pat. No. 5,305,160entitled COMPENSATING FOR VARIATIONS IN TORQUE CAPABILITY OF VOICE COIL MOTORS, issued Apr. 19, 1994 to Funches et al. (VCM torque compensation); U.S. Pat. No. 5,369,345 entitled METHOD AND APPARATUS FOR ADAPTIVE CONTROL, issued Nov. 29, 1994 to Phan et al. (flexure bias force compensation); and U.S. Pat. No. 5,592,340 entitled COMMUNICATION CHANNEL WITH ADAPTIVE, ANALOG TRANSVERSAL EQUALIZER, issued Jan. 7, 1997 to Minuhin et al. (read/write channel filter compensation). All of these references are assigned to the assignee of the present invention.
It will be recognized that changes in external environmental conditions such as temperature, humidity and supply voltage levels can adversely affect the operational performance of a disc drive and that the infrequent or periodic performance of compensation routines such as those disclosed in the above identified references may not provide adequate compensation for such changes in environmental conditions. Moreover, it will be recognized that after a period of disc drive inactivity (such as during an "idle" mode of operation), the data transfer rate of the drive may be adversely impacted for a period of time immediately following a command to transfer data until such time that various compensation parameters can be optimized for the existing environmental conditions. As will be recognized, compensation routines can require a relatively significant amount of time to complete, which can adversely affect the ability of the disc drive to immediately commence with the transfer of data.
In order to address this problem, some prior art disc drives have employed environmental sensors to sense changes in environmental conditions and invoke appropriate compensation routines to adjust the compensation parameters accordingly. However, such an approach undesirably adds significant amounts of further complexity and cost to the disc drives.
Accordingly, there is a need for an improved approach to compensating for changes in environmental conditions associated with a disc drive without adversely impacting data transfer rates of the disc drive.